1. Field of the Invention
The invention relates generally to a device for removing toxic substances from the blood.
2. Description of Related Art
When faced with chronic renal failure, different blood-purification or blood-treatment methods are applied, in which apparatuses are employed to remove those substances which are usually eliminated with the urine, and to withdraw fluids. The predominant method used in hemodialysis (HD) is the diffusive transfer of substances; in hemofiltration (HF), it is the convective transfer of substances across a membrane. A combination of the two methods is called hemodiafiltration (HDF). In peritoneal dialysis (PD), no extracorporeal circuit is needed, and the peritoneum is used as the contact membrane.
Because of the large exchange volumes entailed in the named methods, as well as in continuous arteriovenous HF, continuous veno-venous HF, and in plasma-filtration (PF), there must be a precise balancing of the withdrawn fluid, on the one hand, and of the supplied fluid, on the other hand, and of the volume to be ultrafiltrated over the entire treatment time. Gravimetric and volumetric balancing systems are known from the related art.
German Patent 41 16 178 C1 describes a device for purifying blood, in which a volumetric fluid balancing is performed for HF, HDF, and PF systems. The known hemotherapeutic device has a balancing chamber, which is partitioned by a flexible wall into a first and a second balancing-chamber half, the first chamber half communicating with a filtrate line, and the second chamber half with a substituate line. A filtrate outlet line branches off from the first chamber half to an outlet, while a substituate line, which communicates with the circulatory system, branches off from the second chamber half. The filtrate and the substituate are alternately supplied, as the case may be, to the balancing chamber from an equalization chamber which communicates with the filtrate or substituate line by means of a pressure device. When working with the known filtration device, the equalization chambers are filled by a filtrate pump or a substituate pump and, after the cut-off clamps are opened, are emptied by means of the pressure device into one of the balancing chamber halves. The cutoff clamps are inserted in such a way that when the filtrate flows in, the substituate flows out, whereas when the substituate flows in the filtrate flows out. Accordingly, two pairs of clamps are alternately switched over into the other respective operating position. The drawback is that when only one balancing volume is used, a discontinuous flow occurs, which leads to pulsation.
When the disposable balancing unit is used in PD, the principle applies accordingly. In this case, however, substituate is not continuously balanced with the filtrate, but rather, using additional clamps and connections, fresh dialysate is first supplied via both balancing chamber halves and, after being retained in the abdominal cavity, the consumed dialysate is conveyed in the same manner into the outflow, i.e., there is no direct displacement of substituate through the filtrate, and vice versa. The volumes quantities! are balanced by adding the individual volumes which are carried away removed! or supplied per chamber filling.
German Patent 39 18 078 C2 describes a device for single-needle dialysis, in which a stream of untreated blood flows from the patient to the arterial line during an arterial suction phase, and a stream of treated blood flows back to the patient through the venous line during a venous return phase. It is proposed that an expansion chamber be provided upstream and downstream from the dialyzer and that the device for the single-needle dialysis be operated in four consecutive phases, namely the suction phase, a first transition phase, the return phase and a second transition phase. The chambers arranged upstream and downstream from the dialyzer are simultaneously filled during the suction phase and simultaneously emptied during the return phase.